The present invention relates to a torque responsive motor-drive assembly and more particularly to a torque responsive motor-drive for traverse rods and the like.
Motor operated traverse mechanisms are known in which opening and closing of the traverse mechanism can be initiated either manually by manually operated switches or automatically as by a timer device, photoelectric device, temperature sensing device or the like. In some motor operated traverse mechanisms such as disclosed in U.S. Pat. Nos. 2,912,632; 3,372,599 and 3,672,425, position sensing limit switches are provided to shut off the drive motor when the traverse mechanism has reached a preselected curtain open or curtain closed position. Such position sensing switches not only require proper positioning for actuation by the traverse mechanism at the desired open and closed positions, but also complicate the wiring and, moreover, do not provide any protection for the motor in the event the traverse mechanism is overloaded or becomes stalled intermediate its open and closed positions. Further, if the traverse mechanism holds one of the position sensing limit switches open when the traverse mechanism reaches its open or closed position, provision must be made to enable restarting of the motor in the reverse direction. In some traverse mechanisms such as disclosed in U.S. Pat. No. 3,372,599, a special motor having forward and reverse windings is provided with one winding connected through one limit switch to the power source and the other winding connected through the other limit switch to the power source. In U.S. Pat. No. 2,912,632, a reversible DC motor is used and diodes are connected in parallel with the position sensing limit switches and so arranged that, when the motor drives forward into one of the position sensing limit switches to open it, the motor is deenergized. When the polarity of the voltage is reversed, the associated diode allows the motor to be driven in the reverse direction. Some other motor operated drives for traverse mechanisms such as disclosed in U.S. Pat. No. 3,753,457, use a slip clutche in the motor drive to prevent overloading of the motor. U.S. Pat. No. 3,808,483 discloses a motor drive for a traverse mechanism using a burn-out protected motor.
It is also known to provide torque responsive drives such as disclosed in U.S. Pat. Nos. 2,843,691; 4,085,345 and 4,548,250, in which a pair of torque limit switches are arranged to be operated by a switch actuator to interrupt current to the electric motor when the load on the mechanism driven by the motor exceeds a predetermined load, in either direction of rotation of the motor. Conventional switches have a switch plunger and require a certain amount of travel of the switch plunger before the switch is actuated from one condition to the other, which amount of travel can vary somewhat in different switches. Moreover, conventional switches can only accommodate a limited amount of over-travel of the switch plunger without causing damage to the switch or the switch plunger. It is accordingly necessary to accurately position the limit switches with respect to the limit switch actuator in order to interrupt power to the motor when a predetermined load is exceeded, in either direction of rotation of the motor, and to prevent damage to the switches in the event a sudden or momentary overload causes overtravel of the limit switch actuator. U.S. Pat. No. 3,478,182 discloses a rotary drive mechanism including a torque responsive switch having rotary elements arranged for relative angular movement about the axis of rotation and cam means acting between the elements to effect axial movement therebetween upon relative angular movement, and switch contacts controlled by relative axial movement between the elements.